Exim on potato

About a month ago, I set up a mail server for a local
customer. His ISP provides a wireless service with a firewall at his location.
The firewall is set up to allow email (ports 110 and 25) through to a specific
local IP address.

The setup of Exim went so smoothly that I didn't even
make notes - it worked the first try.

Everything ran fine the first three weeks. Then the ISP
went down. A few days later the customer's site went down due to a local power
failure (the wrong switch was thrown).

Now the customer can send email to:

1. other local users at the local site

2. the ISP

3. others using the ISP

but not to anyone outside the local ISP.

When the customer trys to send to an account outside
the local ISP's control, it receives an immediate 'look-up' error (i.e. DNS
failure). Likewise when an outside account tries to access the customer, they
get an 'account not found' type of error. It is as if they could not find the
user on the email server.

Lastly, the tech that set this up on the ISP's side is gone until
Tuesday.